The guides included quotes, references, and pictures directly from the books assigned. The students had to buy the guides and novels (or audiobooks). I am not sure how the recordings were made, or if they were officially licensed by the publishers. I didn't bring this up with my employers for fear of losing my job. Was I using pirated material? It's possible you're asking because you want to report your ex-employers for copyright infringement. That's not unusual. Disgruntled ex-employees are a major source for reporting intellectual property violations (and they're often rewarded for their reporting).
In any case, we couldn't tell you with any certainty if a copyright owner could pursue an infringement claim. Most likely the unauthorized audio recordings constitute infringement but as for the rest, that depends on the amount taken, whether the use is excused as a fair use, whether the copyright owner can maintain a lawsuit in the foreign jurisdiction (or has a basis for suing in the U.S.), and who committed the alleged infringement.